In a vehicle seat hinge assembly, it is common to have several components that comprise the hinge assembly, including the components that provide for the angle of the seat back, to be controllably adjustable. Most of these components are mass produced from sheet metal by stamping or similar processes. For any one particular component produced in this manner, a range of tolerances in the order of 0.010" can be expected. Resultingly, replications of the same component will be of slightly different sizes. When the vehicle seat hinge assembly is assembled, the various components are placed seriatim one to another and, resultingly, the aforesaid tolerances of the various components stack. Thus, the overall dimensions of the assembled vehicle seat hinge assembly may vary by up to about 0.030", or more.
The stacked tolerances of all of these components can vary considerably from one replication of a given hinge assembly to the next replication of the same type of hinge assembly.
When the various components of a seat hinge assembly are assembled, there is an inherent space, known as "clearance" between each component and any component mating therewith. Clearance is due to differences in size between the various mating components. Clearances between the mating components cause a condition known as backlash. Backlash results, for instance when one component is operatively moved and the clearance between any of the mating components is eliminated such that all of the components are contacting mating components so as to allow for concurrent movement of all of the mating components. Thus, a certain degree of backlash is a necessary characteristic of vehicle seat hinge assemblies and is needed to give the various components of any particular replication of the hinge assembly enough freedom to operatively move with respect to one another. However, excessive backlash, which may result from the stacked tolerances previously described, is undesirable from both the aesthetic and safety standpoints.
Backlash in a vehicle seat hinge assembly typically manifests itself by way of pivotal looseness of the seat back of a vehicle seat with respect to the seat cushion. In one well-known type of manually operable vehicle seat hinge assembly, the seat back is manually released with respect to the seat cushion through operation of a release lever which interacts with a latch pawl pivotally mounted on the seat back. Such a latch pawl is typically mounted on the seat back for selective latching contact with a latch plate associated with the seat cushion. With this arrangement, the seat back may be unlatched to fold forwardly over the seat cushion, which is commonly known in the art as "dumping" of the seat back. Backlash between the latch pawl and the latch plate in the latched configuration of the seat hinge assembly is a major contributor to the aforesaid pivotal looseness of the seat back.
For both aesthetic and safety reasons, the seat back must be held securely in place and relatively immovable with respect to the seat cushion when latched in its upright position. Accordingly, backlash between the seat back and the seat cushion should be minimized when the seat back is latched in its upright position.
The reduction of backlash in vehicle seat hinges has become one of the single most important problems to be overcome by vehicle seat hinge designers in the last decade. One solution widely employed by the industry has been to re-design existing vehicle seat hinges by employing optimized geometry. While such solutions have been partially successful, further improvements in backlash reduction remain necessary and desirable.